Doughnut P.

asked • 11/25/14

Factoring using GCF

So this Section is "solving quadratic equations by factoring", I got the hang of it, but stumped on a few. So one problem says 8y^2 -28y-60 and the answer is 4(2y+3)(y-5). I do not get how they got that though. Because for other problems like 5x^2+5x-10 I came up with 5(1x^2+1x-2) and it seems legit (Did it according to how a site taught iT)
Also troubled on 3x^2+54x+243. The GCF is 3, so I do 3(1x^2+18x+81). Either thats it or I break it down to 3(1x+2x)(1x+9).
Thanks.

Doughnut P.

What about writing quadratic equations in intercept Form and give the functions zeros? one question is y=x2-3x+2. I got it into intercept form but it is incorrect. 
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11/25/14

Mark M.

The zeros of a function are those values of x that make the function zero.
 
0 = x- 3x + 2, factor using FOIL
0 = (x - 2)(x - 1)
 
The two zeros are 2 and 1.
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11/25/14

2 Answers By Expert Tutors

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Mark M. answered • 11/25/14

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Mathematics Teacher - NCLB Highly Qualified

Doughnut P.

Thank you for confirming, although I do not understand how it gets down to 3(1x=2x)(1x+9) on the last one. Or is this not so? What I got prior to this was 3(1x+6x)(1x+27). 
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11/25/14

Mark M.

x+ 18x + 81 is a perfect square trinomial; a2 + 2ab + b2 = (a + b)2
x2 + 18x + 81 = (x + 9)2
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11/25/14

Doughnut P.

This one makes much more sense. Thanks.
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11/25/14

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